Field of the Invention
The invention relates to a metal 3D printer for laminate-molding a three-dimensional object as a product by repeatedly sintering metal powder in a molding chamber. In particular, the invention relates to a metal 3D printer that is provided with a device for removing fumes generated by sintering of the metal powder from the molding chamber.
Description of Related Art
The conventional metal 3D printer forms a thin powder layer by spreading metal powder uniformly on a table, and irradiates a specific irradiation region in the powder layer with a laser beam, so as to form a sintered layer. A desired three-dimensional object is formed by stacking a large number of the sintered layers. The metal 3D printer determines the irradiation region of the laser beam for each division layer that is obtained by dividing the three-dimensional object at a predetermined height. In other words, the metal 3D printer decides the irradiation region for each powder layer. In order to prevent deterioration of the metal powder, it is required to remove oxygen from the atmosphere around the powder layer as much as possible. The conventional metal 3D printer maintains a low oxygen concentration by supplying an inert gas, e.g., nitrogen gas, to the molding chamber enclosing the powder layer.
When the metal powder is irradiated by the laser beam, smoke called “fumes” resulting from aggregation of metal vapor is generated. The fumes soar and spread. The fumes that fill the molding chamber may block the laser beam. As a result, the laser beam carrying the required energy does not reach the irradiation region and causes sintering failure. The sintering operation needs to be suspended till the fumes are eliminated to an extent that does not adversely affect the laser beam. Metal dust is harmful to the human body. Moreover, the fine metal particles in the fumes may fall and mix with fresh powder, and impair the product quality.
Patent Document 1 and Patent Document 2 have disclosed a process chamber having a rectangular parallelepiped shape and a method of carrying the fumes away with a flow of inert gas to remove the fumes from the irradiation path of the laser beam. An inert gas inlet is disposed on the upper side of one side wall of the process chamber while an inert gas outlet is disposed on the lower side of another side wall opposite to the one side wall, so as to create a flow of the inert gas across the irradiation region.
Patent Document 3 has disclosed a metal 3D printer that is capable of creating a local inert gas flow to effectively eliminate fumes from the irradiation path of the laser beam. The metal 3D printer creates the local gas flow by supplying a compressed gas from a supply nozzle that is attached to the wall of the chamber. Alternatively, the local gas flow is created by a fan installed in the chamber.
Patent Document 4 has disclosed a metal 3D printer, in which at least two ventilation channels are formed in the table. One of the ventilation channels supplies the inert gas into the chamber while the other discharges the inert gas to the outside of the chamber. The at least two ventilation channels are connected to an intake pump or an exhaust fan via pipes. According to the invention of Patent Document 4, fumes can be removed actively from the vicinity of the generation source of the fumes.